There are certainly measurable differences between the irons, and by feel, you can tell what you're using when you get used to certain things (coincidentally, I've sharpened a lot of razors, and I've never really loved the eskilstuna steels in razors, but they make nice chisels and plane irons).
But are they material? I have paid a lot of attention to toolmaking from the amateur maker's standpoint, but to efficiency and comfort in dimensioning from the dimensioner's standpoint because I wanted to nail down how to make dimensioning enjoyable - I've done it for the majority of what I've made in the last 10 years and plan to do it as long as I'm physically able. Little things make big differences there. There are two that are monstrously more important than premium plane irons, though, or even good ones. All I really care is that an iron doesn't chip or fold. Anything in the performance gap between those two, I don't really care about (prefer not to have irons full of lots of vanadium that become very difficult to grind and sharpen, but none of the "chrome vanadium" tools actually have much vanadium in them - they have little bits and its for hardenability. Specialty lathe turning high end steels, etc, have lots of vanadium in them for people who like to turn dirty stumps, etc).
The two things that are important:
1) learning to use the cap iron. It halves dimensioning time in wood that's anything other than dead perfect
2) learning to sharpen faster
#1 drastically increases how much wood you can take on a stroke for all middle and fine work, and decreases the need for surface quality dependent on sharpness (uniformity becomes more important). Any decent oilstone will plane anything, even the mid grade ones. Anything, really anything, too - figured bubinga, whatever.
#2 is obvious. once clearance is running out, squeezing more distance out of a plane is very undude when it comes to effort. Sharpening has to be accurate, too, but it's hard to be in the cycle of results and not notice when it's not accurate enough.
Optimizing something like plane iron steels, etc, is kind of a waste of time if it ignores either of the two above. Wear and honing/grinding are related, but there are a whole bunch of other conditions if you're going to maximize laziness (having a whole setup that, for example, both allows fast sharpening but automatically keeps ahead of nicking without doing extra work).
I target a minute to sharpen from totally dull, but to get as good of sharpness as I can get.
Though I like to talk about these details and make tools, I'd call replacing irons that work well a waste of time. Going for a certain feel or characteristic as a matter of interest is something else entirely, though. Kind of like buying expensive furniture. It's not something I'd do, but there have been generations of woodworkers who have benefited from it.
(just for fun reference, my softest older irons are freres and dwight/french (which I think was a US maker). You can almost roll a burr on them, and they may not be very good smoothers in hardwoods - ...ok ,they aren't. But they're wonderful in a try plane or a jack plane because they refresh with almost no effort. Learning to get the greatest volume of work done with a soft iron can teach a lot of useful things that carry over to the more typical good irons (like pre-70s stanley irons. Stanley's 1950s and earlier efforts in the US are wonderful in a cycle of real work).
I made and sold a coffin plane last year (just to try a wear design). Someone on another forum gave me a couple of eskilstuna irons that someone had. To my disappointment, the iron that I had chipped easily even though it didn't seem ungodly hard. I put it away and didn't think about it until I listed the plane.
Someone finally bought it on ebay (chipping mentioned and all - everything will sell if you wait long enough) - and I decided being much farther along that I"d offer to temper it back a little and reharden it if necessary - the buyer agreed. I tempered it back for half an hour in a toaster oven and it was sweet as pie to use. That's going back to mentioning the territory between tough enough (soft enough) and strong enough (hard enough). Good irons generally have a pretty big spread between those two.
There's no way I could measure a volume of work now being competent with planes and dimensioning and point to changing irons (other than outright defective) to improve results or time spent, though. Fascination with planing twice as long is an agreement between the dealers and the people with a 7 minute sharpening routine.